Multi-nozzle liquid droplet ejecting head, a writing instrument comprising such a head, and a method of ejecting liquid droplets from same

ABSTRACT

A liquid droplet ejecting head designed to be mounted in a liquid ejecting instrument that includes ejection nozzles through which droplets are to be ejected from the head, and actuating chambers, each actuating chamber having at least one inlet to be in fluidic connection with a liquid reservoir for providing liquid to the actuating chamber. The ejecting head also includes at least one actuating unit suitable for creating a pulse wave in the liquid contained when activated by energy received from a control device and at least one outlet portion in fluidic connection with at least one ejection nozzle.

CROSS-REFERENCE OF RELATED APPLICATION

This application is a national stage application of InternationalApplication No. PCT/EP2005/010062, filed on Sep. 14, 2005, the entirecontents of which are incorporated herein by reference.

FIELD OF INVENTION

The embodiments of the present invention relate to liquid dropletejecting heads, and to liquid droplet ejecting instruments comprisingsuch heads. More particularly, the embodiments of the present inventionalso relate to methods of ejecting liquid droplets from such liquiddroplet ejecting heads.

BACKGROUND OF INVENTION

More particularly, the embodiments of the present invention relate to aliquid droplet ejecting head designed to be mounted in a liquid ejectinginstrument, comprising a plurality of ejection nozzles through whichdroplets are to be ejected from the head, and a plurality of actuatingchambers, each actuating chamber having at least one inlet to be influidic connection with a liquid reservoir for providing liquid to theactuating chamber, at least one actuating means suitable for creating apulse wave in the liquid contained therein when activated by energyreceived from a control device, and at least one outlet portion influidic connection with at least one ejection nozzle of said pluralityof ejection nozzles.

Prior art is known describing ink ejecting heads containing a pluralityof actuating chambers having one nozzle of ejection for eachink-ejecting actuators, and the nozzles being arranged in a matrixpattern. A plurality of droplets originating from a plurality of nozzlesare then ejected, with each ejected droplet impinging individually ontoa support to create a spaced-apart contact area in the same form as thematrix pattern.

These ejecting heads are generally used in a protected environment wheredrafts of air are minimal, ejecting distances are known and generallystay constant, for example in desk printers. In cases where it has beenprovided for variable scan speed prior art have generally relied onvarying the frequency of ejection to achieve more ink deposition.However, this does not resolve the problem that they still face ofejecting over greater distances.

SUMMARY OF THE INVENTION

The embodiments of the present invention have been conceived inconsideration of the above mentioned drawbacks and proposes an alternatesolution. Thus an object of the embodiments of the present invention isto provide a liquid droplet ejecting device suitable notably forejecting droplets from an ejecting head onto a support at greaterdistance than what conventional devices operate with. To this end anaspect of the embodiments of the present invention is to provide aliquid droplet ejecting head of the above mentioned type characterisedin that the plurality of nozzles are arranged such that the ejecteddroplets combine at a predetermined point situated at a certain distanceaway from the head.

The head retains a classic actuator arrangement, except that the finaldroplet is a result of the combination of a plurality of ejecteddroplets from a number of nozzles. The plurality of ejected droplets cancombine anywhere in the gap existing between the head and the support,or even combine at the point of contact with the support. Bigger, andtherefore heavier, droplets will be ejected, and they will travelfurther and truer than smaller droplets. This is an important advantagewhen using hand-held writing instruments where distances between theliquid droplet ejecting head and the writing surface are generally farlarger than applications where traditional ink ejection technology isused, such as desk inkjet printers.

A further advantage of this configuration is that by combining aplurality of simultaneous droplets together on or before the support, abigger single spot is formed thereon, i.e. without blanks visiblebetween the individual droplets, as can be the case with traditionalejectors. This enables us to draw a thicker line, or to operate the headat a lower ejecting frequency.

It should also be noted that this embodiment of the present inventionallows for the use of typically-sized actuators, such as those used indesktop inkjet printers, to create bigger-than-typical sized drops bycombining many small ejected droplets into bigger final droplets.Because of the smaller actuator size, this allows for greaterpositioning and arranging freedom of the actuators within a liquiddroplet ejecting head.

A supplementary advantage is the possibility to vary the volume of thefinal ejected droplets as a function of user-input or deduced outcome byhaving the option of actuating a different number of actuators at eachink firing, and have a single drop of varying size contact a support.This is especially useful to mark lines of varying thickness withouthaving to vary frequency.

All the while, the structural arrangement remains as in classicaldevices, whereby the path of ink is very direct from the reservoir tothe nozzle, for greater reliability.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Various embodiments of the embodiments of the present invention mayadditionally include any one of the following provisions:

-   -   each nozzle of the plurality of nozzles has an ejection axis,        and wherein the plurality of nozzles are oriented such that        their ejection axis intersect one another at the predetermined        point;    -   the plurality of actuating chambers are arranged in a        substantially radial pattern around a central axis, the        predetermined point being located on said central axis;    -   a plurality of liquid feed chambers are provided, each feed        chamber communicating with the inlet of one actuating chamber        and having at least one through-hole to be in fluidic connection        with a liquid reservoir;    -   the head is substantially flat shaped with a front face and a        rear face, parallel to each other, the nozzles being formed in        the front face, and holes in communication with the inlets of        the actuating chambers being provided on the rear face;    -   the inlets and outlet portions of the plurality of actuating        chambers extend globally in the main plane of the flat body, and        preferentially along radial directions from a central axis;    -   the liquid ejecting head is manufactured out of a silicon wafer        or formed of a thermoplastic material;    -   actuating means comprises one of the following means chosen in        the group including: electrostatic, thermal, piezoelectric        actuating means, and preferably an electrostatic means.

An ejecting head as defined above is particularly suitable to be used ina hand held liquid ejecting instrument having a substantially tubularbody with an opening at a front end and containing a liquid reservoir,an energy storage means, a control unit and a liquid droplet ejectinghead according to any one of the previous provisions.

The hand held liquid ejecting instrument may also further comprise:

-   -   a distance sensing means to determine the distance between said        head and a support and designed to eject the liquid on said        support when said distance is in a predetermined range;    -   the predetermined point is situated at a distance to the head        such that the liquid droplets ejected simultaneously from the        nozzles combine on said support to form a single spot;    -   the predetermined point is situated at a distance to the head        such that the liquid droplets ejected simultaneously from the        nozzles combine to form a single drop before impacting said        support;    -   the liquid ejecting instrument is a writing instrument.

The embodiments of the present invention concern a droplets ejectingmethod for controlling the ejection of droplets by the liquid ejectinghead mounted in a liquid ejecting instrument characterised in that itcomprises the following steps:

-   -   providing a plurality of actuating chambers, each actuating        chamber having at least one inlet (107), at least one actuating        means suitable for creating a pulse wave in the liquid contained        therein, and at least one outlet portion,    -   providing a plurality of ejection nozzles in fluidic connection        with outlet portions of said plurality of actuating chambers,    -   feeding the actuating chambers through their inlet with liquid        provided from a liquid reservoir,    -   actuating simultaneously the actuating means of at least two        actuating chambers of said plurality of actuating chambers by a        supply of energy from a control unit in a manner such that at        least two liquid droplets are ejected through at least two of        said plurality of ejection nozzles,    -   providing an arrangement of said nozzles such that said at least        two liquid droplets combine at a predetermined point situated at        a certain distance away from the head.

In another preferred embodiment, the invention may also additionallyinclude any one of the following steps:

-   -   the simultaneously actuated chambers are chosen among said        plurality such that the droplets are ejected from nozzles which        are arranged equidistant and in equiangular position with        respect to the predetermined point;    -   the method further comprises a step of determining a number of        actuating chambers to be actuated, before the actuating step, to        obtain a final determined droplet size.    -   the instrument is a hand held writing instrument comprising        distance and/or movement sensing means, wherein the liquid is an        ink, and wherein the method further comprises the steps of:        -   determining a writing condition from the signals sensed by            sensing means;        -   ejecting ink droplets repeatedly while a writing condition            is determined, and preferably at constant ejection            frequency;    -   evaluating the final determined droplet size according to a        least one of the parameters of the group including a sensed scan        speed of the instrument, a sensed distance between a surface and        the ejection nozzle, and a desired thickness or style of the        line to be drawn.

DESCRIPTION OF THE DRAWINGS

Other, non-limitative, characteristics and advantages will appear tothose skilled in the art in the following detailed descriptions, inwhich:

FIG. 1 is a sectional representation of a writing instrument comprisingan ejection head according to a first embodiment;

FIG. 2 is a more detailed view of the embodiment in FIG. 1, wherein theejected droplets combine at a point situated before the support;

FIG. 3 is the same view as in FIG. 2 of a second embodiment, wherein theejected droplets combine at a point situated on the support;

FIG. 4 shows a perspective view of the ejection head comprising a coverplate and a base plate.

FIG. 5 shows the same perspective view as in FIG. 4, with the coverplate removed.

On each of the figures, the same reference numerals refer to identicalor similar elements.

FIG. 1 represents a particular embodiment of a liquid droplet ejectinghead 100 mounted in a non-contact writing instrument 1. However, thisembodiment of the present invention is not limited to writinginstruments, and it would be apparent to those skilled in the art thatthis is but one possible embodiment that has equally valid uses inhandheld printers, desktop printers, correction devices, paintingdevices or other instruments which releases liquid onto a supportwithout physical contact between the instrument and the support.

The writing instrument has a substantially tubular element that extendsbetween a front end 11 and a rear end 12 forming a pen. The tubularelement has an inside wall 13 defining a hollow internal space, and anoutside wall 14 designed to be held in the hand of a user.

The interior hollow space of the writing instrument 1 comprises a liquidreservoir 15 mounted in a removable fashion such that it may easily beend-user replaceable, and contains a liquid 16. The liquid used in thisembodiment presented, that of a writing instrument, will have visibleink as its liquid, but depending on the application, the liquid may alsobe correcting fluid, glue or other liquids to suit the application.

At least one fluidic link 130 exists between the liquid reservoir 15 andthe liquid droplet ejecting head 100.

The writing instrument 1 further comprises an energy storage unit 17 toprovide energy to a control unit 20 and a liquid droplet ejecting head100. The energy storage unit 17 may be mounted in the writing instrument1 such that is may be easily replaceable, or it may be integrated withthe liquid reservoir 15 as described in French patent application filedon Jul. 22, 2004 under the application n° FR 04 08138, or have means onthe writing instrument for recharging.

The writing instrument 1 may also comprise other devices such as a meansfor measuring distance between the liquid ejecting head 100 and awriting medium 2, such as with an optical range finder 21, and means formeasuring writing activity of the pen, for example with an accelerometer22.

According to the first embodiment, the liquid droplet ejecting head 100is mounted in the writing instrument 1 facing a front opening 19situated at the frond end 11 of the writing instrument 1. The head isphysically small such that it can be located rear to the front end 11forming the pen tip without causing visual obstruction to the user.

The control unit 20, which comprises a central processing unit, a systemclock, and other parts, serves to process all data such as those ofdistance and writing activity measurements and also to regulate andenergize the energy process provided for the actuation of the dropletejecting head 100 responsible for ejecting liquid 16 out of nozzles 99.

It is also realizable for the control unit 20 to be adapted to onlyeject liquid 16 out of the liquid droplet ejecting head 100 whilemovement is detected through the accelerometer 22, and thatsimultaneously the optical system 21 detects that a distance between thenozzle 99 and the writing medium 2 lies in a range of values defined bya predetermined minimum value and a predetermined maximum value, it mayalso follow the principle of “ink again unless already marked”—that isto say that the optical system 21 would detect whether the surface hasalready been marked and will not further mark it.

As best seen on FIGS. 4 and 5, the liquid droplet ejecting head 100 isdefined by a base plate 101 on which multiple actuating means 120, alsocalled actuators, for ejecting liquid 16 are provided and a cover plate102 placed on the top of the base plate 101 to cover the base plate andthus contain the liquid 16 in the chamber contained therein. The head100 constitutes a front face 110 defined by the top surface of the coverplate 102, and a rear face 111 defined by the bottom surface of the baseplate 101.

The base plate 101 and the cover plate 102 are of a substantially flatrectangular shape, and are manufactured by semi-conductor process usinga silicon wafer, or similar. However, other materials can be used formanufacturing the base and cover plates (101, 102). In particular, thesecomponents of the liquid ejecting head can be formed of a thermoplasticmaterial, like polycarbonate, in order to reduce the cost.

FIG. 5 best shows the base plate 101 with a cut away portion of thecover 102. A plurality of actuating chambers 105 and feeding chambers106 are provided. As it is the case for this embodiment, three feedingchannels 107 establish a fluidic communication between the feedingchamber 106 and the actuating chamber 105 and form the inlets for theactuating chambers 105. The outlet portions 108 of the actuatingchambers 105 provide a fluidic communication between the actuatingchambers 105 and the ejecting nozzles 99. A different number of channelsor different shaped channels 107 are entirely possible, as long as theyfulfill the purpose of delivering liquid from the feeding chambers 106,or directly from the ink reservoir 15, to the actuating chambers 105.

Each nozzle 99 is in fluidic communication with one actuating chamber105 via an outlet portion 108 positioned in the base plate 102. However,it is conceivable to connect two or more nozzles of the plurality ofnozzles to one actuating chamber, or one nozzle with two or moreactuating chambers.

The actuating chamber 105 comprising the actuation means 120 are linkedto the control unit 20 by signal lines (not shown) for energizing anddriving the actuation means 120.

The cover plate 102 is a thin plate in which a central axis X traverses.A plurality of nozzles 99 are positioned on the front face 110substantially radially and equidistant from this central axis X. Eachnozzle 99 of the plurality of nozzles has an ejection axis X1, such thateach ejection axis of the plurality of nozzles 99 intersects one anotherat a predetermined point P. Point P is at a predetermined distancebetween the ejection head 100 and the support 2. FIGS. 2 and 3illustrate two different cases whereby the droplets combine before thesupport (FIG. 2), and on the support (FIG. 3). Point P is thus the pointwhere the plurality of ejected droplets emanating from the plurality ofnozzles 99 combine and continue on to impact the surface 2 and mark asingle spot. The term “combine” refers to a plurality of droplets comingtogether and continuing in unison. The ejected droplets may join totouch each other and continue on a slightly altered trajectory together.Alternatively, they may physically combine to form a single homogenousdrop.

As it is showed on FIG. 5, six actuating chambers 105 are singularlyconnected to six liquid feed chambers 106 and are arranged around acentral axis X in a radial pattern.

Each actuating chamber 105 is substantially sector shaped, however itcan be in any shape accommodating the actuating means 120 and providingan outlet portion 108 in fluidic communication with at least one nozzle99 formed in the cover plate 102. The actuating chambers 105 and thefeeding chambers 106 are equidistant from the centre, and equiangularfrom each other, and extend globally on the same plane of the base plate101. The nozzles 99 are also arranged symmetrically and equiangularlyaround the central axis X. Consequently, the ink drop resulting from thecombined droplets at point P travels along the central axis X and impactthe support 2 with high precision. However, for other reasons, it may beintended to have a deliberate uneven distribution of droplets such thatat point P they combine and continue to impact the support 2 at adivergent angle to the central axis X.

Liquid 16 flows through the actuating chambers, toward the outletportions 108 under energy from pulses emitted by the actuators 120 whichare part of the actuating chambers 105. The actuating chambers 105themselves are supplied with liquid 16 from the liquid feed chambers106. This embodiment has the form of connecting one-to-one actuatingchambers 105 and feeding chambers 106, however it is conceivable to haveone liquid feed chamber 106 connecting more than one actuating chamber105.

The liquid feed chambers 106 are in fluidic communication with theliquid reservoir 15 and temporarily stores a small amount liquid 16,that is allowed to flow from the feed chambers 106 into the actuatingchambers 105.

Furthermore, the fluidic connection channels 107 connecting the feedchambers 106 to the actuating chambers 105 are designed in such a wayfor easing the flow of liquid 16 into the actuating chambers 105 butproviding a much great resistance to backward flow and under a pulsedpressure effected by the actuators 120 from the energy provided by thecontrol unit 20. If the outlet portion 108 constitutes a separateportion to the actuating chambers 105, then a passage to the outletportion should provide as little resistance as possible to the pulsedliquid traversing this part.

An ink supplier hole 109 is located in each liquid feed chamber 106. Theliquid supplier hole 109 is perforated through the thickness of the baseplate 101 and emerges in the rear face 111 of the base plate, which alsoconstitutes the rear face of the ejecting head 100. The hole 109communicates with the liquid reservoir 15.

The embodiment described comprised six actuating chambers 105, howeverany plurality of actuating chambers may be realized with the sameconcept presented herein.

Actuating chambers 105, and more particularly actuators 120, can becontrolled individually, in groups, or all together in parallel. Howeverin practice the actuators 120 are operated in opposite pairs or groups,irrespective of the numbers of chambers present.

In a typical configuration of such a droplet ejecting device 100 asdescribed above, a microscopic droplet pulsed from the actuating chamber105 typically has a volume in the range 25 to 80 pl, such that the totalvolume of all chambers is approximately 150-200 pl.

It is important to note that this concept could be implemented using anyactuating means, including piezoelectric, thermal, or electrostaticactuators.

The most common means of actuating a liquid pulse is with a thermalhead, however it suffers from the disadvantage of limited life. To gosome way towards alleviating this problem of limited life, the controlunit can be configured to rotate the usage of a specific actuator as afunction of previous action to spread the wear evenly across allactuators.

Another actuating means in with piezoelectric actuators. These have theadvantage of having no limitations when used together with nonwater-based liquids. However they suffer in hand-held applications fromthe high-voltages needed for actuation.

The preferred means of actuation is with an electrostatic actuator dueto its high energy efficiency, particularly at small scales. It is notlimited also to water based liquids and only low voltages are needed.

A further embodiment possible under this invention is the ability ofmixing different liquids, for example the ability of mixing differentcoloured inks. Instead of having a liquid reservoir 15 containing asingle colour, one could conceivably separate the reservoir intodifferent containers for different colours, but not necessarily in equalvolumes to take into account different weighing factors or usage rates.A plurality of feeding channels 130 could then be made into the support110 of the liquid ejecting head such that only a subset of the totalnumber of actuator is responsible for each colour. With this embodiment,and using four separate colours comprising cyan, magenta, yellow andblack, it is conceivable that the user could write in any colour, from acombination of the above colours.

Next, a method of ejecting a liquid droplet from the liquid dropletejecting heads 100 according to the embodiments will be described.

As mentioned above, the ejecting head 100 is mounted on the end of awriting instrument 1 for a particular embodiment, and the liquidinstrument 1 comprising a control unit 20, an energy source 17 forpowering the control unit 20, and a liquid reservoir 15.

The ink is stored in either a fixed or replaceable ink reservoir 15 inthe body of the writing instrument 1, and feeds the droplet ejectinghead 100 with ink 16 through at least one fluidic communicating channel130. The liquid feed chamber 106 allows a small individual reserve ofink 16 to be available to its corresponding actuating chamber 105, andthe perforated hole 109 provided in said feed chamber 106 communicateswith the liquid reservoir 15.

The actuator 120 type in the actuating chamber 105 may comprise, but isnot restricted to, the following types: electrostatic, piezoelectric,thermal. This document will not enter into the detailed working of thesedifferent types of actuators as they exist in various embodiments, andthey are well known in the art.

Once the control unit 20 determines it appropriate, the actuators 120 inthe actuating chambers 105 actuates from a pulsed energy input providedby the control unit 20.

This burst of energy would be mostly directed via a path of leastresistance which is towards the centre towards the outlet portion 108. Apulsed wave containing a small amount of liquid 16 will then movetowards the nozzles 99. This liquid-carrying pulsed wave from theactuating chambers 105 will traverse the base plate 101 along the mainplane towards the nozzles 99. The droplets will exit out of the nozzles99 contained in the cover plate 102, and together with other pulseddroplets effected at the same instant of time from other actuatingchambers 105, will combine after ejection from the nozzles 99 at a pointP.

It may be desirable to spread the usage of the actuators 120 such thateach actuator accumulates, on average, approximately the same number ofactuation. This is especially desirable for the thermal-type actuators.

The head 100, and also the control unit 20, must be capable of inking ata sufficiently high frequency such that individual drops of ink are notvisible and the ejection appears continuous. The control unit 20 willtherefore actuate a varying number of actuators 120 at a fixed frequencyof between 500-800 Hz, such as to attain a reasonable drop size on thewriting surface so as to attain a reasonable perceived thickness of thewritten line depending on the scan speed of the instrument 1. A totalcombined drop volume at point P of approximately 150-200 pL is desirablein order to create a reasonable line width on the writing surface 2, forexample 0.3 mm on a single pass.

An advantage of this over having a varying droplet size is that inkingfrequency can be maintained at a reasonable rate to prevent theindividual drops from visibly separating, even if the pen tip movesquickly.

The control unit 20 will determine the number of actuators 120 toactuate to vary line widths as a function of pen scanning speed sourcedfrom internal sensors such as accelerometers 22, or external commandssuch as pressure on the pen grip, or user settings.

The droplets size could be also determined according to the senseddistance between the nozzle 99 and the medium 2 to guarantee an impactof the droplets against the medium 2. It is also possible to vary thedroplets size to vary the thickness of the written line.

1. A liquid droplet ejecting head designed to be mounted in a liquidejecting instrument, comprising a plurality of ejection nozzles throughwhich droplets are to be ejected from the head, and a plurality ofactuating chambers, each actuating chamber having at least one inlet tobe in fluidic connection with a liquid reservoir for providing liquid tothe actuating chamber, at least one actuating means suitable forcreating a pulse wave in the liquid contained therein when activated byenergy received from a control device, and at least one outlet portionin fluidic connection with at least one ejection nozzle of the pluralityof ejection nozzles, wherein each ejection nozzle has an ejection axis,wherein the plurality of ejection nozzles are oriented such that theejection axis of each nozzle intersects with one another at apredetermined point situated on a central axis of the head at a certaindistance away from the head so as each ejection axis forms an angle withthe central axis, the ejected droplets combine at the predeterminedpoint, and wherein the control device is configured to actuate theactuating chambers at a fixed frequency between 500-800 Hz, theplurality of actuating chambers being arranged to pulse a total combineddrop volume of approximately 150-200 pL.
 2. The liquid droplet ejectinghead according to claim 1, wherein the plurality of actuating chambersare arranged in a substantially radial pattern around a central axis,the predetermined point being located on the central axis.
 3. The liquiddroplet ejecting head according to claim 1, wherein a plurality ofliquid feed chambers are provided, each feed chamber communicating withthe inlet of one actuating chamber and having at least one through-holeto be in fluidic connection with a liquid reservoir.
 4. The liquiddroplet ejecting head according to claim 1, wherein the head issubstantially flat shaped with a front face and a rear face, parallel toeach other, the nozzles being formed in the front face, and holes incommunication with the inlets of the actuating chambers being providedon the rear face.
 5. The liquid droplet ejecting head according to claim4, wherein the inlets and outlet portions of the plurality of actuatingchambers extend globally in the main plane of the flat body, andpreferentially along radial directions from a central axis.
 6. Theliquid droplet ejecting head according to claim 5, wherein the liquidejecting head is manufactured out of a silicon wafer or formed of athermoplastic material.
 7. The liquid droplet ejecting head according toclaim 6, wherein actuating means comprises one of the following meanschosen in the group including: electrostatic, thermal, piezoelectricactuating means and an electrostatic means.
 8. A hand held liquidejecting instrument having a substantially tubular body with an openingat a front end and containing a liquid reservoir, an energy storagemeans, a control unit and a liquid droplet ejecting head according toclaim 1, wherein the plurality of ejection nozzles of the ejection headfaces out of the front opening of the tubular body.
 9. The hand heldliquid ejecting instrument according to claim 8, further comprising adistance sensing means to determine the distance between the head and asupport and designed to eject the liquid on the support when thedistance is in a predetermined range.
 10. The hand held liquid ejectinginstrument according to claim 9, wherein the predetermined point issituated at a distance to the head such that the liquid droplets ejectedsimultaneously from the nozzles combine before or on the support to forma single spot.
 11. The hand held liquid ejecting instrument according toclaim 9, wherein the predetermined point is situated at a distance tothe head such that the liquid droplets ejected simultaneously from thenozzles combine to form a single drop before impacting the support. 12.The hand held liquid ejecting instrument according to claim 8, whereinthe liquid ejecting instrument is a writing instrument.
 13. The liquiddroplet head according to claim 1, wherein the plurality of ejectionnozzles comprises several ejection nozzles which are arrangedequidistant with respect to the predetermined point.
 14. The liquiddroplet ejecting head according to claim 13, wherein the angles withrespect to the central axis of each ejection axis of the severalejection nozzles are identical.
 15. The hand held liquid ejectinginstrument according to claim 9, wherein the predetermined point issituated at a distance away from the head such that the liquid dropletsejected simultaneously from the nozzles combine before a support beingat a distance in the predetermined range.